It is known to combine the screw cap of a nail polish bottle with an applicator brush. The cap functions as a closure for the bottle and as a handle for the applicator brush. However, prior art nail polish bottle caps are not well suited for use as the handle of an applicator brush.
In particular, the relatively small size of the cap compromises handling and control of the applicator brush. A small cap may only be grasped between the fingertips of the user and as a result, translational slip of the fingertips along the longitudinal axis of the cap occurs. This type of slip makes it difficult for the user to uniformly apply a detailed brush stroke onto the small surface area of a fingernail. In addition, the applicator cap of prior art nail polish bottles will have a non-angular transverse cross section i.e. it is round or otherwise provided with a curved surface. This curvature contributes to rotational slip of the fingertips as the cap is twisted onto or off of the bottle. Threading the cap on the bottle is especially difficult when nail polish applied to the users nails has not fully dried and the cap is being held lightly between the users fingertips.
Anatomical differences among users may also contribute to a poor grip on the applicator cap. Variation in finger size and shape means different users grasp the cap at different locations along the length of the cap in an effort to optimize their grip. A user having short and thin fingers is more likely to grasp and squeeze the cap near the end secured to the brush whereas a user having larger fingers may find it necessary to grip the cap at a more central location or further away from the end secured to the brush. As is apparent, grasping the cap at different locations along the length of the cap affects the grip on the cap and therefore control of the brush stroke.
Fatigue is yet another problem. To achieve a smooth brush stroke and uniform application of a coating of polish, a user tends to squeeze the cap. This application of pressure by the fingertips against the cap functions to stabilize the users hold as the user effects a sweeping motion with their hand. Repeatedly applying and releasing pressure against the cap will eventually cause fatigue and discomfort.
The material from which the cap is constructed also contributes to fatigue and a poor grip. Nail polish bottle caps are constructed from rigid and hard plastics. The exterior surface of a cap constructed from hard and inflexible materials is uncomfortable to hold over any extended period of time and as noted earlier, when the cap is repeatedly squeezed between the fingertips during use, the hard surfaces accelerate the feeling of discomfort and fatigue. Although the exterior surface of some prior art caps may be provided with ridges or similar raised structures in an effort to improve the grip against the hard and smooth surface of the cap, such efforts are known to diminish comfort.